The present invention relates to a novel optical rotator of high efficiency and large area useful in the fields of display, opto-electronics and optics and capable of being produced and handled easily.
A rotating property of the direction of the vibration of polarizing light is called an optical rotatory power, and substances which exhibit such property are known as optical rotator. In the field of optics or opto-electronics there is used an optical element called an optical rotator for the purpose of causing an azimuthal rotation of linear polarization or of elliptic polarization by utilizing such optical rotator. Typical examples are a 1/2 wavelength plate, an optically active crystal plate, and various phase plates. These are formed by grinding an optically active crystal such as rock crystal or a birefringent crystal such as calcite. Although these optical elements are highly accurate, an advanced technique is required for the manufacture thereof, and the cost is high. One having a large area cannot be manufactured and it is difficult to them for general purposes. On the other hand, as such optical element of low cost there are various phase films obtained by stretching plastic sheets. Although these films can be formed to have a large area, there is the problem that the accuracy thereof is poor. Further, in both the use of a birefringent crystal and a stretched plastic sheet, it is only at a predetermined single wavelength that the optical elements exhibits its function basically in high efficiency.
If there is obtained an optical rotator which permits a high accuracy in the wide range of wavelengths and in the fields of display, opto-electronics and optics, the usefulness thereof will be great to an immeasurable extent.
It is the object of the present invention to provide an optical rotator having such characteristics.
If a twisted nematic liquid crystal structure can be realized using a liquid crystalline polymer and immobilized as a transparent film, it becomes possible to attain high accuracy and large area which has heretofore been impossible, and by the optical rotator power of such twisted structure it is made possible to obtain a highly versatile, optical rotator in the wide range of wavelengths. Taking note of the foregoing properties as an optical rotator of the twisted nematic liquid crystal structure and also taking note of the point just mentioned above, the present inventors have made extensive studies and finally accomplished the present invention.